A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
The lithographic apparatus may be provided with an actuator to position an object. For example, the actuator may position an object, such as a substrate table or a support. To have a fast response time it may be beneficial to mount the actuator with high stiffness to the object. With such stiff mount, thermal expansion by heating up of the actuator may cause deformation of a part of the actuator that is stiffly mounted to the object and thereby deformation of the object itself. Since the object may need to be positioned with high precision a deformation of the object may jeopardize positioning of the object. Heating up may also be caused by other heat sources such as the illuminator beam, other actuators in the assembly, heating elements, fluids flowing through the structure etc.